We should have a special category on this blog for words you’ll likely never, ever have any cause to use. Case in point, the word circumjovialist: a specific term for a satellite of the planet Jupiter.
The “circum–” part here is fairly straightforward; it’s the same root as found in words like circumference, circumambulate (“to walk all the way around something”), circumambient (“all-surrounding”), and circumbendibus (“a roundabout way of doing something”). Etymologically, the prefix circum– comes from the Latin word circum, which literally means “around” or “in a circle” (and is ultimately a fairly close relative of circus, in the sense that circus performances take place in a ring).
The “–jovial” part here is a little more confusing, and something more of a story to tell.
As an adjective in its own right, jovial, meaning “mirthful” or “jolly,” has been in use in English since the early 1600s. Before then, it was used to mean “inhabiting, resembling, or else occurring under the influence of the planet Jupiter”; the two are connected because qualities of mirthfulness and jolliness were once associated with the influence of Jupiter in astrology.
Etymologically, jovial comes from Jove, an old poetic name for Jupiter; the name Jupiter itself, incidentally, is a corruption of the Latin Jovus pater, or “father Jove”, as Jupiter was the chief male deity in Roman mythology.
Put these two elements together, then, and you have circumjovial—a word, with roots in Roman mythology, for anything that orbits the largest planet in our solar system.